April 15, 1923: Insulin becomes broadly available.

While Stacey McGill will probably be the first kidlit or YA character with diabetes to leap to many minds, she's not the character I immediately think of. No, the first character I think of is Pete Hautman's Lucy Szabo from Sweetblood. Because she's got a great voice and a hugely entertaining take on her diabetes: 

It seems clear to me that diabetes in the Middle Ages led to the folktales that led to Bram Stoker's book that led to Anne Rice's novels and Buffy the Vampire Slayer and all the other vampire stuff. Diabetics were the original, the real vampires. They weren't evil or superpowerful or immortal. They were just sick. Like me. I'm actually a proto-vampire. When I take an insulin shot now, I think of it as vampire vaccine. If I quit taking insulin altogether I would become that starving vampire girl from the Middle Ages. I might come crashing into your house and eat your pork stew.

Or whatever.

Love her. I should re-read that one.

Other characters? I can't think of many. Uncle Lester in The Cardturner, the grandmother in No Safety in Numbers, girls in a couple of Lurlene McDaniel books... Oh, and I think that the main character in Butter has diabetes, but I haven't read it yet. (THOUGH I REALLY, REALLY WANT TO. MUST ILL IT SOON.)

Others?